N-long-chain acyl acidic amino acid and/or a salt thereof have long been known to be useful as less irritant materials as compared to conventionally-used skin or hair cleansing compositions containing an anion surfactant such as alkylsulfate, alkylsulfonate and the like as a main component.
However, addition of N-long chain acyl glutamic acid and/or a salt thereof to skin and hair cleansing compositions containing alkylsulfate, alkylsulfonate, polyoxyethylene alkylether sulfate and the like as a main agent for the purpose of reducing the irritation problematically decreases the viscosity.
To solve this problem, attempts have been made to thicken N-long-chain acyl acidic amino acid-containing cleansing agents by the addition of an ester or ether polymer thickener having a polyoxyethylene chain (JP-A-6-158089), addition of a polysaccharide thickener (JP-A-6-264090) and addition of a cellulose natural polymer derivative (JP-A-2003-55690). However, addition of a sufficient amount of a polymer thickener to ensure viscosity has resulted in new problems relating to the sense of use, such as poor foaming, sliminess during rinsing, which is characteristic of polymers, and the like.
In an effort to thicken N-long-chain acyl acidic amino acid-containing cleansing compositions, moreover, addition of colloidal silicate to an aqueous solution of N-long-chain acyl acidic amino acid salt has been known, though a sufficient viscosity as a liquid cleansing composition cannot be achieved (JP-A-7-11288).
On the other hand, as gel compositions containing a N-long-chain acyl acidic amino acid and/or a salt thereof, a gel composition having thixotropy (JP-A-6-057290), and an aqueous thickening gel composition and a liquid oil-in-water emulsion composition (JP-A-9-301846) have been reported. They are used as base materials for the production of skin external agents such as cosmetic serum, cream and the like, which contain N-long-chain acyl acidic amino acid and/or a salt thereof. However, since these aqueous thickening gel compositions and liquid oil-in-water emulsion compositions do not have a foaming power or a cleaning power, a sufficient function as a skin and hair cleansing composition has not been achieved.
Thus, a thickening composition containing n-long-chain acyl acidic amino acid and/or a salt thereof, which shows suitable thickening performance without impairing the foamability and sense of use of n-long-chain acyl acidic amino acid and/or a salt thereof has been strongly desired.